The evaluation of calcium channel blocking drugs, Verapamil, Diltiazem, Nifedipine and Lidoflazine, on platelet aggregation indicated an inhibitor by Verapamil and Diltiazem to aggregation by epinephrine. Further evaluations of cyclic AMP levels indicated that Diltiazem appears to increase platelet levels of cAMP whereas Verapamil does not. Competitive binding studies assessed the adrenergic receptor interactions with these drugs. The effects of Dantrolene will be studied by the Quin-2 method for monitoring internal calcium levels in platelets. Cyclic AMP levels in response to Vanadate and Ristocetin will also be evaluated.